Analysis of the effect of surface texture in light-emitting diodes based on a finite-difference-time-domain method

We used a two-dimensional finte-difference-time-domain (FDTD) method to study the effect of surface texture in light-emitting diodes (LEDs). Surface texture is implemented as a rectangular groove, dividing the high index medium and the low index medium. The transmission efficiency of the dipole source located in the high refractive index medium is measured with various parameters of the rectangular groove. The transmission efficiency of the roughened surface increases about 36% compared to that of the smooth surface. As for the period of the groove ranging from 0.5λ to 2.5λ, the efficiency does not show much dependency on the period or duty cycle. On the other hand, the transmission increases with the depth of the grooves. Extraction efficiency improves 78% when the depth of the grooves reaches twice the period. The amount of efficiency increase is significant considering that the grating period is much larger than that of photonic crystals. Furthermore, the weak dependency of transmission efficiency on the period and on the duty cycle of the grooves may alleviate processing difficulties by increasing fabrication tolerance of surface texture.